M.Celino¹, M.Gusso¹, S.Giusepponi¹, T.Deutsch², I.Duchemin², U.Aeberhard³, P.Czaja³,
A.Walker⁴, S.Islam⁴, D.Ghosh⁴, M.Salanne⁵, D.Borgis⁵, M.Levesque^5
1 ENEA; ²CEA; ³Jülich; ⁴ University of Bath; ⁵ Maison de la Simulation

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Introduction
Computational materials modelling plays a crucial role in the design of devices for efficient low cost energy generation and storage by allowing the characterization of materials down to the atomic scale. The accuracy of predicted macroscopic quantities depends on the atomic scale models describing the interatomic forces and how they are implemented on larger length and time scales. Despite its large demand on computer resources, materials modelling has a considerable impact in research and industry areas. Applications, for example inorganic and organic photovoltaics (PV), supercapacitors and batteries, benefit from atomic and meso scale design to understand and improve charge transfer at molecular level. The main objectives are:

• To provide a set of computational routines for morphology, electronic structure and transport properties of energy-related materials for PV, batteries and supercapacitors;
• To set up a screening methodology for designing materials for PV, rechargeable batteries and supercapacitors with optimal energy conversion and storage capabilities;
• To demonstrate how the computing infrastructure can address challenging problems in the field of energy by focussing on their atomic scale origin.

To fulfil the WP objectives three application lines have been set up. An application line is a WP3 transversal activity that composes the available numerical methods and models to better address a full characterization of a technological application (in this project PV, batteries and supercapacitors). The development of the application line approach will allow to extend this methodology to other energy technologies. Moreover numerical tools and methodologies for exascale are developed to support the application lines deployement.

Development of an atomic structure of a-Si, a-Si:H and interface a-Si:H/c-Si.
The silicon hetero-junction (SHJ) technology holds the current efficiency record of 25.6% for silicon-based single junction solar cells and shows great potential to become a future industrial standard for high-efficiency crystalline silicon (c-Si) cells. The a-Si:H/c-Si interface, while central to the technology, is still not fully understood in terms of transport and recombination across this nanoscale region, especially concerning the role of the different localized tail and defect states in the a-Si:H and at the a-Si:H/c-Si interface and of the band offsets and band bending induced by the heterostructure potential and the large doping, respectively.

Development and porting of methods for force-field parametrization.
Development and porting of methods via charge analysis to facilitate the parametrization of the force fields using DFT. This will be applied to organic ions and also to batteries (interaction between graphite-like electrode and the electrolyte). The linear scaling version of BigDFT builds an optimized localized atom-centered basis set for each atom expressed on Daubechies wavelets basis sets. Then the Hamiltonian, the overlap matrix and the density matrix can be expressed in this optimized localized basis set, and are sparse reducing considerably the cost of calculations. We can, actually, use this minimal basis set to express other quantities and doing, for instance, a charge analysis which is the natural way to compare with polarizable force elds. Charge analysis is the key quantity to perform QM/QM or QM/MM calculations using a polarizable force field.

Metadynamics.
Classical MD and DFT methods are used to address bulk and nanostructural properties of new perovskite materials for solar cells alongside electrode and solid electrolyte materials to enhance their energy density. Perovskite cells suffer from hysteresis due to the motion of iodide vacancies. Existing molecular dynamics codes have diculty in isolating this motion from that of the nonmobile ions. Metadynamics is being investigated as a way of addressing this problem.

Atomic structures for batteries and supercapacitors.
Batteries and supercapacitors play complementary roles in the field of energy storage. While the former are characterized by large energy densities, which makes them suitable for many applications such as in electric vehicles, supercapacitors show better power densities and are therefore used when fast charges/discharges are needed. Both devices would highly benet for a better understanding of the atomic structure of the solid materials and of the liquid electrolytes which are involved. In this project, we focus on the family of LLZO solid electrolytes for Li-ion batteries and on the study of nanoporous carbon-based electrodes for supercapacitors.

Ab-initio electronic and photonic structure.
Based on the atomic structures the present Task aims to develop efficient real-space embedded density functional theory and many-body perturbation theories (MBPT= GW, Bethe-Salpeter) for accurate ab-initio descriptions of the electronic and optical properties of the active part of organic and hybrid systems (interfaces, defects, dopants, etc.) while fully accounting for the effect of the environment (solvent, dielectric, electrodes, etc.). The real-space formulation allows a description of electron and exciton hopping energies to feed mesoscale analysis.

EoCoE offers an ever-expanding NETWORK of experts in High Performance Computing and in Sustainable Energies from Academia, Industry and the Public Sector. EoCoE services are now online: to improve numerical applications, to use new cutting-edge numerical tools and to take advantage of consultancy and training services.

Reports

Deliverable 3.1

Contact

Massimo Celino (ENEA): massimo.celino@enea.it